There have been variously proposed stencil printers where print is made by driving, for instance, a thermal head according to image data obtained by reading out an original by, for instance, a scanner to selectively melt and perforate stencil material to make a stencil, winding the stencil around a printing drum, supplying ink inside the printing drum, and transferring the ink to printing papers through the stencil by, for instance, a roller.
In the stencil printers described above, a stencil material roll into which the stencil material is rolled is employed to improve the operability. However, the surface smoothness of the stencil material roll to be brought into close contact with the thermal head deteriorates as compared with the surface smoothness of the stencil material in the form of a sheet before it is rolled for, for instance, the rolling pressure when the stencil material is rolled into a roll. The deterioration of the surface smoothness increases toward the core of the stencil material roll and increases as the elapsed time from the production thereof increases. When the surface smoothness of the stencil material deteriorates, the thermal head is variously brought into contact with the stencil material and sites easy to perforate and sites difficult to perforate are generated in the stencil material, whereby the quality of the printed images deteriorates. In order to overcome this problem, there has been proposed, in Japanese Unexamined Patent Publication No. 2002-79646, a method where fluctuation in perforation is avoided by visually or optically detecting the surface condition of the stencil material and controlling the heating energy to the thermal head according to the detected surface condition of the stencil material.
However, the method disclosed in Japanese Unexamined Patent Publication No. 2002-79646 is disadvantageous in that visual detection of the surface condition of the stencil material is limited and setting of the suitable heating energy to the thermal head is sometimes impossible, and optical detection of the surface condition of the stencil material adds to the overall size of the system and to the cost of the system.
In view of the foregoing observation and description, the primary object of the present invention is to provide a thermal head control system which can control the heating energy to a thermal head according to the surface condition of the stencil material without adding to the overall size of the system or to the cost of the system.